ESTIMATION AND

CLASSIFICATION OF

RESERVES OF PETROLEUM

OVERVIEW

Reserves(Petroleum) are the amount of crude oil,

natural gas that can be produced profitably in the

future from subsurface reservoirs

Making a good estimate of recoverable resources is

crucial to a company’s financial position since future

recovery is a measure often used to ascertain a

company’s borrowing future worth.

Depending on the scope of their operation, operators

of oil and/ or gas properties require estimates of

reserves and judgment about the degree of uncertainty

in those estimates

Of concern in the estimation and classification of

reserves are:

• Potential resources of crude oil

• Volume and degree of uncertainty of reserves on prospects being developed,

• Sizing and design of equipment to process reserves and transport them to market, and

• Opportunities for additional profit from incremental reserves that might be attributable to stimulation of producing wells,infill drilling, equipment modifications or additions, or improved recovery projects

Overview (2)

UNCERTAINTIES IN RESERVOIR ESTIMATES

Estimates of oil and/ or gas from subsurface reserves are controlled to

a significant degree by the heterogeneities of the reservoir

The degree of uncertainty in estimates of reserves depends

mainly on

The degree of geologic complexity

Maturity of the property,

The quality and quantity of geologic and

engineering data,

The operating environment, and

The skill, experience and integrity of the

estimators

Definitions of Petroleum Fluids

• Petroleum is a general term to apply to all

naturally occurring mixtures of predominantly

hydrocarbons. Petroleum includes natural gas ,

crude oil, and natural bitumen.

• Crude oil is the portion of petroleum that exists

in the liquid phase in natural underground

reservoirs and remains liquid at atmospheric

conditions of temperature and pressure

Classification crude oil

• Crude oil may be subclassified as: extra heavy

(stock-tank gravity less than 10° API), heavy

(stock-tank gravity 10 to 22.3°API), MEDIUM

(stock tank gravity 22.3 to 31.1°API).

• Crude oilk also has been classified as

naphtheric, mixed base, or paraffinic. This

classification is based on a characterisation

factor determined from density and atmospheric

boiling point curves.

Classification natural gas

• Natural gas may be subclassified as

associated or nonassociated gas.

Associated natural gas is found in contact

with or dissolved in, crude oil in a natural

underground reservoir.Nonassociated

natural gas is found in a natural

underground reservoir that those not

contain crude oil

Classification

• Solution gas, also(incorrectly) called

casing head gas is natural gas that is

dissolved in reservoir oil under initial

reservoir cnditions of pressure and

temperature and that is liberatedfrom

solution by reduction in pressure and

temperature as the oil is produced through

surface gas/oil separation equipment

Classification

• Lease condensate

Also called condensate or distilllate, is a

petroleum liquid consisting mostly of

pentanes and heavier that is in the

gas(vapor) phase under initial reservoir

conditions and that condenses to the liquid

phase when the gas is produced

Classification

• Plant Products

Plant products are petroleum liquids and associated products that have been extracted from lease gas at a central plant generally utilising absorption and/ or refrigeration processes. Plant product typically include ethane, propane, butane, and heavier components reffered to as natural gasoline

CLASSIFICATION OF RESERVES

• Because reserves of oil and/or gas are the commercially recoverable portion of accumulations of fluid hydrocarbons in the spaces of rocks, estimates of reserves should always be qualified to indicate the degree of uncertainty. The most used qualifiers are “proved,””probable”and “possible,”

• Generally procedures to estimate and classify reserves(ECR) have been described as deterministic or probabilistic

methodology

deterministic Procedures

Typically use the “best estimate” of the “true

value” of each relevant imput parameter in

a data set to calculate for each data set, a

single “best estimate” of reserves. Such

reserves, or part of such reserves, may be

classified as proved, probable, and/ or

possible.

Probabilistic Procedures

Typically use the full range of potential

values of each relevant input parameter in

a data set to calculate, for each data set, a

set of reserve estimates that reflect the

frequency distribution of the basic data.

Lehee’s Classification

A. Proved